That's not a simple fire. That's the "Will of Fire". An Ultimate Artifact that - awh, all right. That's just a bonfire. Perhaps that's how the angels get their wings to glow. They all carry a bonfire around and place it behind them so they look shining and glamorous. Riiiiight?

"There’s nothing to fear but fear itself and maybe some mild to moderate jellification of bones." Cave Johnson, Portal 2.